Water

South Bank University Graphic

Water's chemical description is H2O, that is one atom of oxygen bound to two atoms of hydrogen. The hydrogen atoms are "attached" to one side of the oxygen atom, resulting in a water molecule having a positive charge on the side where the hydrogen atoms are and a negative charge on the other side, where the oxygen atom is. 

Since opposite electrical charges attract, water molecules tend to attract each other, making water kind of "sticky." The side with the hydrogen atoms (positive charge) attracts the oxygen side (negative charge) of a different water molecule.

• Water is unique in that it is the only natural substance that is found in all three states -- liquid, solid (ice), and gas (steam) -- at the temperatures normally found on Earth. Earth's water is constantly interacting, changing, and in movement.
• Water freezes at 32^o Fahrenheit (F) and boils at 212^o F (at sea level, but 186.4^° at 14,000 feet). In fact, water's freezing and boiling points are the baseline with which temperature is measured: 0^o on the Celsius scale is water's freezing point, and 100^o is water's boiling point. Water is unusual in that the solid form, ice, is less dense than the liquid form, which is why ice floats. Water contracts until it reaches 4 C then it expands until it is solid. Solid water is less dense that liquid water because of this.
• Water has a high specific heat index. This means that water can absorb a lot of heat before it begins to get hot. This is why water is valuable to industries and in your car's radiator as a coolant. The high specific heat index of water also helps regulate the rate at which air changes temperature, which is why the temperature change between seasons is gradual rather than sudden, especially near the oceans.
• Water has a very high surface tension. In other words, water is sticky and elastic, and tends to clump together in drops rather than spread out in a thin film. Surface tension is responsible for capillary action, which allows water (and its dissolved substances) to move through the roots of plants and through the tiny blood vessels in our bodies.
•  water's properties:
  • Weight: 62.416 pounds per cubic foot at 32^°F
  • Weight: 61.998 pounds per cubic foot at 100^°F
  • Weight: 8.33 pounds/gallon, 0.036 pounds/cubic inch
  • Density: 1 gram per cubic centimeter (cc) at 39.2^°F, 0.95865 gram per cc at 212^°F

The States of Water

Water has three states. Below freezing water is a solid (ice or snowflakes), between freezing and boiling water is a liquid, and above its boiling point water is a gas. 

 Water changing from solid to liquid is said to be melting. When it changes from liquid to gas it is evaporating. Water changing from gas to liquid is called condensation . Frost formation is when water changes from gas directly to solid form. When water changes directly from solid to gas the process is called sublimation.

Water Measurements

  1 gallon = 4 quarts = 8 pints = 128 ounces = 231 cubic inches
  1 liter = 0.2642 gallons = 1.0568 quart = 61.02 cubic inches
  1 million gallons = 3.069 acre-feet = 133,685.64 cubic feet

Source:

Three temperature scales are in common use in science and industry. 

Two of those scales are SI metric:

The degree Celsius (°C) scale was devised by dividing the range of temperature between the freezing and boiling temperatures of pure water at standard atmospheric conditions (sea level pressure) into 100 equal parts. Temperatures on this scale were at one time known as degrees centigrade, however it is no longer correct to use that terminology. [In 1948 the official name was changed from "centigrade degree" to "Celsius degree" by the 9th General Conference on Weights and Measures (CGPM).]

The kelvin (K) temperature scale is an extension of the degree Celsius scale down to absolute zero, a hypothetical temperature characterized by a complete absence of heat energy. Temperatures on this scale are called kelvins, NOT degrees kelvin, kelvin is not capitalized, and the symbol (capital K) stands alone with no degree symbol. [In 1967 the new official name "kelvin" and symbol "K" were set by the 13th General Conference on Weights and Measures (CGPM).]

The degree Fahrenheit (°F) non-metric temperature scale was devised and evolved over time so that the freezing and boiling temperatures of water are whole numbers, but not round numbers as in the Celsius temperature scale.

Some baseline temperatures in the three temperature scales:

Water Distribution

• The total water supply of the world is 326 million cubic miles. A cubic mile of water equals more than one trillion gallons. 

• About 3,100 cubic miles of water, mostly in the form of water vapor, is in the atmosphere at any one time. If it all fell as precipitation at once, the Earth would be covered with only about 1 inch of water. 

• The 48 contiguous United States receives a total volume of about 4 cubic miles of precipitation each day.

•  Each day, 280 cubic miles of water evaporate or transpire into the atmosphere. 

• Of the freshwater on Earth, much more is stored in the ground than is available in lakes and rivers. More than 2,000,000 cubic miles of fresh water is stored in the Earth, most within one-half mile of the surface. Contrast that with the 60,000 cubic miles of water stored as fresh water in lakes, inland seas, and rivers. The most is stored in the 7,000,000 cubic miles of water found in glaciers and icecaps, mainly in the polar regions and in Greenland.

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Credit: EPA, UNEP, USGS, NASA